The Universal Serial Bus Attached SCSI (UAS) protocol transfers commands and data from external disk drives with a Universal Serial Bus (USB) interface. UAS improves upon the existing Bulk-Only Transport (BOT) protocol to allow the host (e.g., a personal computer) to queue multiple commands on the device. However, UAS requires the storage device to transfer all the data for a command before transferring data for any other command. Indeed, in a device with multiple hard disk drives (HDDs), it is possible for two or more HDDs to be ready to transfer data, but a UAS device would only service one HDD's data transfer while making the other HDDs wait until the first one was finished.